Nearly four times as slow! And that is just one simple numeric index. I see tables with twenty or thirty indexes: wide compound indexes, complex function based indexes. The effects on high volume DML may be devastating. Of course this simple not very scientific test may not apply to your environment, but it serves to emphasize the point that indexes have a cost. Be sure that you really need them.
Tests done using DB release 12.1.0.2, Windows 10, Dell laptop with SSD disc.
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John Watson
Oracle Certified Master DBAhttp://skillbuilders.com